The increased circuit densities defined in semiconductor chips has increased the need for more effective cleaning of the semiconductor wafers from which the clips are made. A widely-used method for cleaning silicon semiconductor wafers is the use of a hot acid bath, such as sulfuric acid, into which a reagent chemical such as hydrogen peroxide, has been added. Because the sulfuric acid is highly reactive, conventional plumbing and agitation apparatus cannot be used within the cleaning bath. Thus, it is common to use a magnetic stirrer for agitating the bath and a chemical dispense head for introducing the hydrogen peroxide into the bath. The magnetic stirrer comprises an elongated ferromagnetic element coated with TEFLON (a trademark for a synthetic resin polymer) that is introduced into the bath; another ferromagnetic element outside the bath is rotated by a conventional motor which causes rotation of the magnetic stirrer in the bath to promote agitation, as is required for removal of reacted contaminants from the wafer surfaces. The chemical dispense head, which is not immersed in the bath, and can therefore be made of conventional materials, typically comprises a pipe with several nozzles for projecting the hydrogen peroxide onto the upper surface of the sulfuric acid bath. Magnetic stirrers and chemical dispense heads as described are commercially available from the Modutek Company, 960 Remillard Court, San Jose, Calif. This system must be operated with care because the highly reactive cleaning chemicals can injure the operators.
There has been for some time a recognized need for a more effective cleaning method than that provided by the conventional system. The U.S. patent of McConnell et al., U.S. Pat. No. 4,778,532, issued Oct. 18, 1988, is an example of relatively expensive and cumbersome apparatus for cleaning semiconductor wafers more effectively. There is therefore still a need for relatively safe, inexpensive and convenient methods and apparatus for more dependably and more thoroughly cleaning semiconductor wafers.